Pilot Columns Research Articles

Fluoride removal in batch and column systems using bonechar produced in a top-lit updraft drum gasifier and furnace

Hundreds of millions of people are exposed to excessive levels of fluoride in drinking water, predominately in low-resource communities. Activated alumina is recognized as the best available technology for fluoride removal from drinking water by the United States Environmental Protection Agency, but it has substantial economic and environmental costs. Bonechar is a more environmentally friendly and potentially lower cost alternative adsorbent. Here, fluoride adsorption from groundwater (pH 8.1 ± 0.2) by activated alumina was compared with bonechar primarily produced from bovine bones at peak heating temperatures between 400 and 1100 °C in a modular top-lit updraft drum (TLUD) stove (using a bone-wood mixture) and furnace. TLUD and furnace bonechar produced at peak heating temperatures 650–1000 °C and 400–800 °C, respectively, outperformed activated alumina in batch tests (i.e., required smaller doses to achieve 90% fluoride removal). The impact of using bovine versus swine bones to produce bonechar had a negligible impact on fluoride adsorption. A wide range of peak heating temperatures in the TLUD achieved by varying primary air flow rates and fuel selection (e.g., bone-to-wood mass ratios) produced efficient fluoride adsorbents. This finding demonstrates that a TLUD can be a robust, operationally flexible production system. Fluoride removal by TLUD and furnace bonechars showed strong, negative correlations (R2 ≥0.88) with organic matter content. Bonechar pilot column tests indicated that the mass transfer zone was captured (i.e., immediate fluoride breakthrough was not observed) at an empty bed contact time (EBCT) of 5 min, increasing EBCT to 30 min had a minimal impact on adsorption efficiency, and intermittent operation (3–10 d shut-off periods) decreased effluent fluoride concentrations. Furnace bonechars produced at peak heating temperatures 400–700 °C outperformed activated alumina in pilot columns. Differences in adsorption efficiencies in batch and column tests were associated with the linearity of fluoride adsorption. A theoretical model quantifying adsorption linearity with Freundlich 1/n values was able to predict adsorber performance solely based on batch test data.

Leveraging DOM UV absorbance and fluorescence to accurately predict and monitor short-chain PFAS removal by fixed-bed carbon adsorbers

Carbon adsorbent fouling by dissolved organic matter (DOM) inhibits the ability of the widely-used rapid small-scale column test (RSSCT) to accurately predict the removal of organic micropollutants (OMP) from water by full-scale carbon adsorbers. Here, the adsorption of 11 short-chain per-/poly-fluoroalkyl substances (PFAS) from groundwater, surface water, and wastewater was examined in pilot columns as well as RSSCTs using constant diffusivity (CD) and proportional diffusivity (PD) designs. Neither the CD- or PD-RSSCT accurately predicted pilot adsorber breakthrough of PFAS using standard diffusional mass transfer models. However, PFAS breakthrough relative to optical property (e.g., peak C, UV absorbance at 254 nm) breakthrough remained constant between pilot column, CD-RSSCT, and PD-RSSCT designs. This finding permitted accurate breakthrough predictions for the sum of PFAS and for 9 of the 11 PFAS on an individual basis in pilot columns using RSSCTs. Multiple linear regressions incorporating influent and treated water optical parameters enabled the modeling approach to be applied to water sources with heterogeneous DOM characteristics. It is hypothesized that this methodology was successful because (i) optical parameters adequately quantified the competitive nature of DOM and their adsorption behaved similar to OMP and (ii) competitive adsorption by low-molecular weight DOM was the predominant fouling mechanism. An OMP monitoring approach was developed for waters containing DOM with heterogenous characteristics that also relied on raw and treated water optical properties. UVA254 and fluorescence monitoring could therefore enable water treatment to remove PFAS in a variety of scenarios that face inhibitory cost and analytical limitations, such as decentralized and low-resource settings.

Fixed-Bed Adsorption Comparisons of Bone Char and Activated Alumina for the Removal of Fluoride from Drinking Water

Fluoride is commonly found at elevated concentrations in groundwaters worldwide and is difficult to remove even with activated alumina (AA) adsorption, the best available technology. Consequently, alternative treatment technologies for fluoride removal continue to be researched, including the use of bone char (BC) adsorption. However, BC studies are limited mostly to batch or equilibrium studies, which can be difficult to extend to full-scale applications. Therefore, the goal of this study was to compare a BC to a commercial AA for treating groundwater with a naturally occurring fluoride concentration of 8.5 mg/L using pilot- and bench-scale fixed-bed adsorption tests. At the pilot scale using an empty bed contact time (EBCT) of 10 min, fluoride breakthrough reached 1.5 mg/L within 450 bed volumes (3.1 days) and 650 bed volumes (4.5 days) for BC and AA, respectively. Two designs of the rapid small-scale column test (RSSCT) were applied to simulate the pilot columns, where the proportional diffusivity RSSCT (PD-RSSCT) design provided a more adequate prediction of fluoride breakthrough to 1.5 mg/L. The PD-RSSCT was also used to evaluate BC and AA EBCTs of 10 and 20 min, with the longer EBCT providing no significant increase in adsorbent use efficiency. Complete BC regeneration using countercurrent flow to the PD-RSSCT was limited by exposure to the sodium hydroxide regenerant solution and, potentially, the presence of arsenic.

Soil aquifer treatment to meet reclaimed water requirements.

To increase the opportunities and reduce the cost of indirect potable reuse, soil aquifer treatment (SAT) was evaluated at the City of Los Angeles' Donald C. Tillman Water Reclamation Plant (DCTWRP) in a 2.5-year pilot study. Six soil columns were operated between February 2016 and November 2018 treating DCTWRP effluent. The goal was to reduce the dissolved organic carbon (DOC) in the effluent to lower concentrations in order to increase the allowable volumes for reclamation. An integrated part of the study was to evaluate the biodegradability of organics in different waters using biodegradable (BDOC) analyses. BDOC has been used in similar research in the past, and in this research, BDOC was an accurate predictor of column performance in removing organic carbon. The total organic carbon in tertiary DCTWRP effluent was reduced from 7 to 10mg/L to 0.9 to 2.5mg/L through a process train beginning with ozonation of the tertiary effluent, followed by biological activated carbon, and finally to the soil column effluents. Additional short-term treatments including reverse osmosis, additional ozonation, and low-pressure UV were also evaluated. The soil columns removed N-nitrosodimethylamine to detection limits. Finally, results from SAT and BDOC were used to develop a kinetic model to predict biodegradation of organic matter of wastewater origin through a soil aquifer system. PRACTITIONER POINTS: Soil aquifer treatment is often used in indirect potable reuse projects to protect aquifers. Soil aquifer treatment was simulated in six pilot columns for 2.5years. Columns were fed tertiary effluent from a nutrient-removal type-activated sludge plant. Effluent TOC was reduced from 10mg/L to 0.9 to 2.5mg/L, and nitrosodimethylamine (NDMA) was also removed. Biodegradable organic carbon analyses accurately predicted soil column performance in removing organic carbon.

Hydrodynamics and mass transfer performance of vapor–liquid flow of orthogonal wave tray column

In the present work, hydrodynamics and mass-transfer performance of vapor–liquid flow of orthogonal wave tray (OWT) column was studied. Dry pressure drop, operating range (capacity graph) and overall column efficiency of OWT column were investigated using pilot columns. A three-dimensional CFD model was developed within the two-phase Eulerian framework to have an insight into the two-phase flow and mass-transfer behavior of OWT. The simulated results were compared with experimental data and showed a good agreement. Hydrodynamic and mass-transfer behaviors were revealed with the aid of velocity profiles, streamlines, interfacial area density distribution and so on. The effects of vapor/liquid load (FS factor) on the Murphree tray efficiency were also studied. The simulations of OWT with different waves showed that the pressure drop, clear liquid height, froth height and Murphree tray efficiency increase with the increase of slope, and OWT with middle slope tended to have more uniform foam layer. Comparison of the liquid-phase component velocity between OWT and ripple shows that OWT has better performance in froth layer distribution and stability. The mass-transfer data showed that OWT not only had almost the same “peak efficiency” as sieve tray, but also had higher capacity and stability, it was suitable for capacity expansion.

Performance of a system with full- and pilot-scale sludge drying reed bed units treating septic tank sludge in Brazil.

This study investigated the performance of sludge drying reed beds (SDRB) at full- and pilot-scale treating sludge from septic tanks in the city of Belo Horizonte, Brazil. The treatment units, planted with Cynodon spp., were based on an adaptation of the first-stage of the French vertical-flow constructed wetland, originally developed for treating sewage. Two different operational phases were investigated; in the first one, the full-scale unit was used together with six pilot-scale columns in order to test different feeding strategies. For the second phase, only the full-scale unit was used, including a recirculation of the filtered effluent (percolate) to one of the units of the French vertical wetland. Sludge application was done once a week emptying a full truck, during 25 weeks. The sludge was predominantly diluted, leading to low solids loading rates (median values of 18 kgTS m(-2) year(-1)). Chemical oxygen demand removal efficiency in the full-scale unit was reasonable (median of 71%), but the total solids removal was only moderate (median of 44%) in the full-scale unit without recirculation. Recirculation did not bring substantial improvements in the overall performance. The other loading conditions implemented in the pilot columns also did not show statistically different performances.

Impact of UV-H2O2 Advanced Oxidation and Aging Processes on GAC Capacity for the Removal of Cyanobacterial Taste and Odor Compounds.

Cyanobacteria and their taste and odor (T&O) compounds are a growing concern in water sources globally. Geosmin and 2-methylisoborneol (MIB) are the most commonly detected T&O compounds associated with cyanobacterial presence in drinking water sources. The use of ultraviolet and hydrogen peroxide (H2O2) as an advanced oxidation treatment for T&O control is an emerging technology. However, residual H2O2 (>80% of the initial dose) has to be removed from water prior final disinfection. Recently, granular activated carbon (GAC) is used to remove H2O2 residual. The objective of this study is to assess the impact of H2O2 quenching and aging processes on GAC capacity for the removal of geosmin and MIB. Pilot columns with different types of GAC and presence/absence of H2O2 have been used for this study. H2O2 removal for the operational period of 6 months has no significant impact on GAC capacity to remove the geosmin and MIB from water.

Quantitative estimates of gas maldistribution and methods for their localization in absorption columns

In the present work, we carry out evaluation of gas flow maldistribution in different types of gas distributing devices (GDD) and packings by using experimental data for the output velocity profiles for both the absorption pilot column and industrial column. Two GDD construction types—with circular and with local tube gas feed, together with their modifications—are investigated. Two pilot columns—with random packing RSRM 1.5″ and with structured ceramic Honey-comb packing, and one industrial contact economizer with Honey-comb and inclined rings—have been studied. Six types of quantitative estimations of GDD and packings maldistribution are determined by the help of MATHCAD. Then, their sensitivity toward several factors, such as the type of GDD and packing, the initial gas flow velocity, the number and dimension of measuring cells on the column cross-section, the measurement error, and so on, is investigated. It is found that only two of the quantitative maldistribution estimations take into account the formation of maldistribution clusters, which deteriorates the uniform gas distribution. A novel method for quantitative determination of these clusters and also for identification of the zones at column cross-section, in which they appeared, has been developed. It is established that the measurement error and the dimension of measuring cell deeply influence the number, the area, and spatial distribution of these zones on the cross-section, as well as the values of maldistribution estimates.

Modelling reactive absorption of CO 2 in packed columns for post-combustion carbon capture applications

A rate-based process model for the reactive absorption of carbon dioxide (CO 2) from a gas mixture into an aqueous monoethanolamine (MEA) solution in a packed column is developed. The model is based on the fast second-order kinetics for the CO 2–MEA reactions and takes into account the mass transfer resistances. The heat effects associated with the absorption and chemical reaction are included through energy balances in the gas and liquid phases. Appropriate correlations for the key thermodynamic and transport properties and for the gas–liquid mass transfer are incorporated into the model to ensure reliable predictions. The model predictions are validated by simulating a series of experiments conducted in pilot and industrial scale absorption columns with random and structured packings reported in the literature. Comparisons between the simulation results and the experimental data reveal good quality predictions of the gas phase CO 2 and MEA concentrations and the liquid temperature along the column height. The sensitivity studies reveal that the correlations for the gas- and liquid-film mass transfer coefficients given by Onda et al. (1968) provide better predictions than the penetration theory of Higbie (1935) and the correlation of Bravo et al. (1985).

Ultra scale‐down approach to correct dispersive and retentive effects in small‐scale columns when predicting larger scale elution profiles

Ultra scale-down approaches represent valuable methods for chromatography development work in the biopharmaceutical sector, but for them to be of value, scale-down mimics must predict large-scale process performance accurately. For example, one application of a scale-down model involves using it to predict large-scale elution profiles correctly with respect to the size of a product peak and its position in a chromatogram relative to contaminants. Predicting large-scale profiles from data generated by small laboratory columns is complicated, however, by differences in dispersion and retention volumes between the two scales of operation. Correcting for these effects would improve the accuracy of the scale-down models when predicting outputs such as eluate volumes at larger scale and thus enable the efficient design and operation of subsequent steps. This paper describes a novel ultra scale-down approach which uses empirical correlations derived from conductivity changes during operation of laboratory and pilot columns to correct chromatographic profiles for the differences in dispersion and retention. The methodology was tested by using 1 mL column data to predict elution profiles of a chimeric monoclonal antibody obtained from Protein A chromatography columns at 3 mL laboratory- and 18.3 L pilot-scale. The predictions were then verified experimentally. Results showed that the empirical corrections enabled accurate estimations of the characteristics of larger-scale elution profiles. These data then provide the justification to adjust small-scale conditions to achieve an eluate volume and product concentration which is consistent with that obtained at large-scale and which can then be used for subsequent ultra scale-down operations.

Influence of the acid buffering capacity of different types of Technosols on the chemistry of their leachates

The preparation of tailor-made Technosols from wastes may be a novel and prospective option for the re-use of wastes and restoration of degraded areas. A two-month study with pilot columns was conducted to evaluate the influence of the acid buffering capacity of different Technosols on the chemistry of their leachates. The Technosols were made from mixtures of organic and inorganic wastes at a ratio of 56:44 (w/w). The organic components used were an anaerobic (AN) and an aerobic (AE) sewage sludge. The inorganic wastes used – referred to as “conditioners” – were Linz-Donowitz slag (LD) and foundry sand (FS). A mixture of the two conditioners at a ratio of 50:50 (w/w) was made to provide a third type of conditioner (LD + FS). Controls consisted of columns filled with organic waste only (either AN or AE sludges). Changes in pH, electrical conductivity, concentrations of major ions and dissolved organic carbon in the leachates were evaluated periodically. The main processes determining the pH of the systems were nitrification and leaching, but organic matter decomposition and carbonation may also have had an influence. Nitrification was strongly retarded in the AN sludge (attributed to the probable absence of nitrifiers in this waste after the AN wastewater treatment) and was impeded in those mixtures in which LD was used as a component (due to the liming effect). Final pH values ranged from 5.0 and 5.4 (in AE and AE + FS, respectively) to 11.1 (in AN + LD). The pH of the other mixtures finally ranged between 7 and 8. In formulating mixtures of wastes, their acid buffering capacity should be taken into account in addition to the nutrient contents and the limits of contaminants established by local regulations.

Hydrodynamic and metallurgical characteristics of industrial and pilot columns in rougher circuit

In this investigation, a pilot-scale flotation column was successfully designed, installed and tested in rougher circuit of the Miduk copper concentrator, Iran. The axial dispersion model was employed in the design procedure. Collection zone rate constant ( k c) along with the target recovery of over 75% was used to size the column. The rate constant k c was determined based on a number of pilot and industrial experiments. Performance of the pilot column was compared with existing full-scale Microcel columns in a number of parallel experiments.

A novel technology for packing and unpacking pilot and production scale columns

A new method of packing and unpacking large scale chromatography columns is described. This involves use of a 3-position valve that can inject chromatography media into a closed column thereby packing it. This same valve in another state is then used to unpack the column. Heights equivalent to a theoretical plate and asymmetry factors of packs on columns from 280 to 800 mm diameter are discussed.

Measurement of residence time distribution of the gas phase in flotation columns

The gas phase residence time distribution in flotation columns was investigated experimentally by the impulse response method using a radioactive tracer gas (Krypton-85). The experimental methodology consisted of introducing an impulse of radioactive gas inside the air sparger using a specially designed device, and on-line measurement of the transient response at various levels in the column. This technique was first tested in a pilot column of 10(cm) diameter and 8(cm) height. Tests were made at 0.8–0.9–1.0–1.5 (cm/s) superficial gas rates and 0-10-20 (ppm) frother dosage. Afterwards, the gas phase of an industrial column of 0.91 (m) diameter and 15 (m) height, operating in a molybdenite cleaning circuit, was studied. Tests were made at 1.3–1.7–2.1 (cm/s) superficial gas rates and 0.7 (cm/s) superficial tailing rate. The transient response curves from pilot and industrial columns showed a typical gas residence time of about 2–4 (min), and the gas dispersion number was about 0.1 and 0.4, respectively. The gas phase in the froth zone behaved closer to a plug flow while operating at superficial gas rates lower than 1.5(cm/s) and superficial wash water rates of 0.2–0.4 (cm/s). A significant gas short-circuiting into the tailing flowrate was clearly observed in the industrial column.

Evaluating Capacities of GAC Preloaded with Natural Water

Adsorption studies are conducted to determine how preloading a natural groundwater onto GAC affects the adsorption of cis-1,2-dichloroethene in small-scale and pilot-scale columns. Capacities are determined from batch-isotherm tests, microcolumns, and pilot columns, which are preloaded for various lengths of time. Breakthrough profiles from short-bed adsorbers and pilot columns provides information regarding the kinetics of adsorption. Some of the results are: adsorption capacity and kinetic rate decreases with increasing time of preloading, the preloaded microcolumns shows capacity reductions similar to that of the preloaded pilot columns, and preloaded column capacities are represented well by preloaded isotherms. The reduction in pilot-column capacity due to preloading for cis-1,2-dichloroethene is shown to be partially offset by using columns in series where the columns are only added when needed to contain the mass-transfer zone. For cis-1,2-dichloroethene, the increased run time due to adding columns may not be worthwhile in field applications, unless extensive preloading occurs before the contaminant arrives at the column.

Field Performance of Activated Carbon Adsorption for Sewage Air

Sewage air at the inlet works of a municipal wastewater treatment plant, was simultaneously pumped through two pilot columns, one filled with an alkali‐impregnated carbon material, while the other was filled with a nonalkali‐impregnated grade. Odor and H2S concentrations at the influent and effluent ports of the carbon columns were continuously monitored for about eight months. The odor and H2S concentrations of the influent sewage air varied significantly throughout the study period, averaging 120SOU/m3 and 5.3 ppm, respectively. Breakthrough of odor at the effluent ports occurred earlier than that for H2S, and the initial breakthrough odor was exerted mainly by non‐H2S compounds. Although the alkali‐impregnated carbon was capable of removing a much larger quantity of H2S than the nonalkali‐impregnated grade, its effectiveness in removing other odorous but non‐H2S gaseous compounds was less significant. The cost of using nonalkali‐impregnated activated carbon for odor removal was comparable to that of th...

Evaluation of flotation column scale-up at Mount Isa mines limited

In late 1987 Mount Isa Mines commissioned a circuit of 3, 2.5 × 13 m flotation columns to upgrade a bulk Pb/Zn rougher concentrate (low grade middlings). The decision was based on the results of extensive testing in a pilot unit (0.05 × 10 m), involving amenability tests and scale-up parameter estimation. The circuit has performed well and the achieved and expected metallurgy are compared. The pilot column was re-run in parallel with the flotation column circuit. This revealed the importance of operating the pilot and plant columns at similar gas rates for comparative results. The circuit generally exceeded the pilot results; possible reasons are discussed.

Distribution profiles of chloroform, weak organic acids, and PCBs on granular activated carbon columns from Waterford, New York

Profiles are given for the distribution of chloroform, weak organic acids, and polychlorinated biphenyls (PCBs) on granular activated carbon (GAC) samples from four pilot columns, placed in series and operated for 26 weeks at Waterford, NY. Chloroform and the weak organic acids are found at or near saturation through most of the GAC system, whereas the PCBs are accumulated only at the inlet. The extent of saturation achieved by these compounds is consistent with differences in their mass inputs and GAC capacities. However, irregularities in adsorption of these substances are evident in localized depletions of chloroform and the weak organic acids at the inlet to the system. Displacement of chloroform from the GAC inlet after 26 weeks' operation is confirmed by analysis of breakthrough data for the trihalomethanes.